Ecosystems and interdependence between the organisms and ... coastal estuary is subsidized by ... Ecosystems are composed of a variety of abiotic and biotic components that

Chapter

2Ecosystems

2.1 ECOLOGY

Ecology is the science that deals with the various principles, which govern the relationship and interdependence between the organisms and their environment. The term “ecology” was coined by combining two Greek words, oikos (meaning house) and logas (meaning the study of) to denote such relationships and interdependence between the organisms and environment. The term ecology has been defined in various ways. Some important definitions are: (i) The ecology has been defined as the study of structure and function of ecosystem. It

may be stated in simple term “It is the study of structure and functions of nature”. (ii) G.L. Clarke (1954): Ecology is the study of interrelations of plants and animals

with their environment, which includes the influences of other plants and animals as well as those of the physical features.

(iii) L.R. Taylor (1967): Ecology is the study of the way in which individual organisms, populations of some species and communities respond to these changes.

(iv) C.J. Krebs (1985): Ecology is the scientific study of interactions between organisms and nature that determine the range/distribution and abundance of organisms.

2.1.1 Objectives of Ecology

(i) To study the relationships between living organism and environment. (ii) To provide the true understanding of the structure and functions of the vast

nature. (iii) To analyze the independence between organisms and environmental

components. (iv) To evolve scientific approaches for controlling and regulating the welfare of living

organisms. (v) To provide the comprehensive awareness of all the relations between all the living

organisms and their all environments. (vi) To evolve mathematical models to relate interaction of environmental components

and predict their effects by employing system analysis approach.

Ecosystems 27

Terrestrial ecosystem: It is often defined by the vegetation type that dominates the community. Terrestrial vegetation has a rapid change of oxygen, water and carbon dioxide. Example, Grassland.

Aquatic Ecosystem: It is further subdivided as freshwater ecosystem and marine ecosystem. There are two types of freshwater ecosystems: (a) Running water (lotic) e.g., river and (b) Stationary water (lentic) e.g., lake. The example of marine water isdeep seas.

Artifi cial ecosystem

Artificial ecosystems are maintained artificially by man. A pond constructed as a part of wastewater treatment plant is an example of artificial ecosystem.

2.2.2 Types of Ecosystem based on Energy Resources

Following are the important ecosystems based on the resources:

Unsubsidized natural solar powered ecosystem

In these types of ecosystem, the only source of power is solar energy. These are unsubsidized in the sense that there is no auxiliary source of energy available to supplement solar energy. On human point of view, these ecosystems are most important because here large volumes of air are purified, water is recycled and climates are controlled, e.g., grassland.

Subsidized natural solar powered ecosystem

In these types of ecosystem, the main source of energy is the sun that is augmented by natural non-solar energy. An extra amount of energy is available to the system that can be used for the production of more organic matter. The other auxiliary natural source of energy may be winds, wave or rain. Example, coastal estuary is subsidized by energy of tides and wave, the back and forth movement of water does a part of necessary work of recycling minerals and nutrients and transporting food and waste.

Man subsidized solar powered ecosystem

In these types of ecosystem, auxiliary fuel or energy like labour and machine is supplied by man. For example, in agriculture, the energy input may be in the form of fertilizers, animals and labour.

Fuel powered ecosystem (Urban-industrial ecosystem)

In these ecosystems, the sun energy is replaced by highly concentrated potential energy of fuel like chemical or nuclear fuel. These are men’s wealth generating ecosystem, e.g., cities.

2.2.3 Structure of a Complete Ecosystem

Ecosystems are composed of a variety of abiotic and biotic components that function in an interrelated fashion (Fig. 2.1).

28 Environment and Ecology

Abiotic component

It is the non-living component of ecosystem and includes: (a) physical or climatic factors such as soil, temperature, light and water; and (b) chemical factors constituting the inorganic and organic substances. The inorganic substances include carbon, hydrogen, phosphorus, potassium, nitrogen and sulphur that are involved in mineral (nutrients) cycle. The organic substances include carbohydrates and proteins.

Biotic component

It includes the living components of the ecosystem and is made of many different populations of species, which are interdependent upon each other in the ecosystem. The living components of the ecosystem are further subdivided as: 1. Autotrophic component: It is the component in which the fixation of light energy,

use of simple inorganic substances and build-up of complex organic substances predominate. The members of autotrophic components are producers, which are self-nourishing.

2. Heterotrophic component: It is the component in which utilization, rearrangement and decomposition of complex organic substances predominate. The members of heterotrophic components are called consumers, which are dependent on others for food. The heterotrophic components are further subdivided as:

(i) Macroconsumers: These are heterotrophs, which occur in an order in a food chain as herbivores, carnivores and omnivores.

(ii) Microconsumers (saprotrophs): These are also known as decomposers such as bacteria and fungi. They feed on organic compound of dead or living protoplasm of plants and animals for their food and energy. They absorb some of the decomposition products and release inorganic compounds in the ecosystem, making them available again to the producers.

2.2.4 Functions of Ecosystem

The functioning of biotic and abiotic components of different ecosystems is so closely interrelated that sometimes it becomes difficult to demarcate between them. An ecosystem performs the following functions (Fig. 2.2): (i) It allows the flow of biological energy, controls the rate of production, respiration

of community. (ii) It controls the rate of nutrient cycle production and consumption of minerals. (iii) It regulates the environment by organism and the organism by environment. For

example, nitrogen fixing by bacteria is the process of environment process and photoperiodism is the process of organism regulation by environment.

(iv) It allows the circulation of chemical elements from environment to organism and back to the environment. In this way it provides nutrients to the producers, which build-up organic matter.

Ecosystems 29Ecosystem

Abiotic component

Physical orclimatic factors

Chemical factors

Soil Light TemperatureWater

Inorganicsubstances

Organicsubstances

Hydrogen Sulphur Phosphorus Potassium Nitrogen

Biotic component

Autotrophiccomponent

Green plants Heterotrophiccomponent

Macroconsumers

Microconsumers

Lion Deer Bacteria FungiCarbohydratesProteins

Fig. 2.1 Structure of an ecosystem

To soil andenvironment (nutrients H,

N, O, C, P, S,K, etc.)

Nutrient pool (soil and environment)

Energy

Energy (food)

EnergyConsumers

Organic matterDecomposers

Producers

Fig. 2.2 Function of ecosystem

2.3 FOOD CHAIN

In an average ecosystem, food is the source of energy. It is obtained from plants and consumed by different categories of consumers. Thus, the transfer of food energy occurs in repeated stages in which it is being eaten by a source of organism. This sequence of eating and being eaten is termed food chain.

Grass Cow Tiger

Algae Insects Fish Man

Ecosystems 31

Fig. 2.5 Terrestrial food web

Fig. 2.6 Aquatic food web

Algae

Rotifers

Aquatic insects

Turtles

Small fish

Large fish

Water fleas

Tadpoles

Second Trophic Level

Herbivores which are primary consumers fall in this category. They get energy by eating the producers.


Fig. 2.7 Trophic level

Sun

Energy

Trees, level 1(Producers)

Rabbit, level 2Grasshopper,

level 2

Grass, level 1(Producers)

Snake,level 4

Birdlevel 3

Hawk, level 5

Third Trophic Level

Carnivores which are secondary consumers fall in this category. They depend on primary consumers for their food energy.

Fourth Trophic Level

Omnivores which may be tertiary consumers fall in this category. They depend upon secondary consumers for energy. Trophic classification does not employ the categorization of species. All organisms taking food in same number of steps come under the same trophic level. According to the source of food assimilated, a given species may occupy one, two or more trophic levels.

2.5 ECOLOGICAL PYRAMIDS

Ecological pyramids are the diagrammatic representation of trophic structure in which the trophic levels are depicted in successive stages.

2.5.1 Types of Ecological Pyramids

There are three types of ecological pyramids:Pyramids of numbers: The numbers of individual organism at different trophic levels in an ecosystem are depicted. The length of the bar at different levels represents the number of organisms at that particular trophic level. It is expressed in number per unit area (Fig. 2.8).

Ecosystems 33

Pyramids of biomass: It is based on the total dry weight of the total amount of living matter. It is expressed in gram per unit area (Fig. 2.9).Pyramid of energy: When the production of a community is measured in terms of energy, it is known as pyramid of energy. It is expressed in calorie per unit area per year. There is always a gradual decrease in energy content at successive level from the producers to consumers.

2.6 ECOLOGICAL SUCCESSION

It means ecological development. It refers to the process of gradual change in conditions of environment and the replacement of older species over the time undergoes automatically. The occurrence of ecological succession has following characteristics: (i) It is a systematic process that involves changes in species structure. (ii) The changes are directional and take place as a function of time. (iii) The succession occurs due to changes in physical environment and population at

the species.

Fig. 2.8 Pyramids of numbers

Tertiaryconsumers(carnivores)

(a)


Secondaryconsumers(carnivores)

Primaryconsumers(herbivores)


Producers



Producers

(c)

(b)



Producers

Bacteria Fungi ActinomycetesHyper-parasiteson liceand bugs

Parasites onherbivores

Herbivores

Producers

Fruit-eatingb rdsi

Lice andbugs

(d)


Carnivores

Herbivores

Producers(a)

Carnivores

Herbivores

Producers(b)

Carnivores

Herbivores

Producers

(c)

Fig. 2.9 Pyramids of biomass

Fig. 2.10 Pyramids of energy

(iv) The changes also occur due to population explosion of the species. (v) The changes are predictable.

2.6.1 Types of Succession

There are following two types of succession:Primary succession: This is the initial stage of development of an ecosystem. It begins with the creation (birth) of a community (species) on such a location, which was previously unoccupied by any living organism. Such location may be water, land, a new island and


Continuing cause: These are responsible for changes in population. Reasons: (i) Migration for industrialization and urbanization (ii) Migration for safety against outsider aggregation (iii) Feeling of competition.Stability causes: These causes bring stability to the community. Reasons: (i) Climatic conditions of the area (ii) Fertility of agricultural land.

2.6.3 Climax

In this, the final terminal community becomes more or less stabilized for a longer period of time, which can maintain itself in equilibrium with the climate of the area. The final community is called climax stage. The climax community is the most complex and stable, providing food and variety of niches for animals. The climax community can tolerate the conditions created by itself, and there are no more successful species to replace them. Following are theoretical approaches to the climax:Monoclimax theory: This theory was developed largely by Federick Clements. It recognizes only one climax, determined solely by climate, no matter how great the variety of environmental condition is at the beginning. The monoclimax theory was supported by Cowles, Ranganathan, and Puri, but strongly objected by Daubenmire (1968).Polyclimax theory: This theory was developed by Tansley. It considers that the climax vegetation of a region consists of not just one type but a mosaic of vegetational climaxes controlled by soil moisture, soil nutrients, topography, slope exposure, fire and animal activity.Climax pattern hypothesis: This theory was developed by Whittaker, Macintosh and Sellack. According to this theory, the composition, species structure and balance of a climax community is determined by the total environment of the ecosystem and not by one aspect, such as climate alone.

2.6.4 Signifi cance of Ecological Succession

(i) Its knowledge helps in maintaining a specific biotic seral stage by interfering the process of biotic succession, e.g., maintenance of teak forest.

(ii) Dams are protected by preventing siltation and biotic succession. (iii) It gives information about the techniques to be used during reforestation and

afforestation.

2.7 INCOMPLETE ECOSYSTEM

Almost all ecosystems have all basic components, viz., producers and consumers. It is possible for a ecosystem to lack one or more basic component.


Ecosystem Diversity: Depending upon the availability of abiotic resources, an ecosystem develops its own community of living organisms. That is why, there exists vivid varieties of ecosystem and they differ widely from each other. Example: A lake ecosystem is different from an ocean ecosystem and a forest ecosystem is different from an urban area ecosystem. This biodiversity is assessed at the continental or global level. Importance of ecosystem diversity (i) Consumptive values: food, fodder and fuel (ii) Productive values: timber (iii) Option values: keeping future possibilities open (iv) Existence values: knowledge and appreciation (v) Ethical and moral values: importance for all forms of life.

2.8.2 Measuring Biodiversity

Diversity of different species varies widely. For some species it may be rich (more), and for others it may be poor. Therefore, to assess the number of species and their evenness, different geographical scales are adopted. These are given as follows:Alpha diversity: This scale is used to determine the ‘number of species in a single community’. It is used to compare with the number of species of other community. This is the diversity within the space.Beta diversity: This scale is a measure of ‘change in composition of a species’ with respect to changes in environment. This is the difference of diversity between habitat.Gamma Diversity: This scale refers to the ‘rate at which the species with similar habitat’ expand from one geographical area to another. This includes the differences over a large area such as a continent. Thus, alpha diversity implies ‘species richness’, beta diversity refers to ‘susceptibility to change’, and gamma diversity means ‘mobility over larger areas’.

Site 1

Site 3 Site 4

Site 25 Species

5 Species 3 Species

3 Species

Fig. 2.11 Alpha, Beta and Gamma diversity

Ecosystems 39

Alpha diversity is measured locally, at a single site as site 1 and 2. Site 1 has higher alpha diversity than site 2. Beta diversity measures the amount of change between two sites or along a gradient, as in regions X and Y. Region Y has higher beta diversity than region X, as there is a higher turnover of species among the sites in region Y. Gamma diversity is similar to alpha diversity, only measured over a large scale. Both alpha and beta diversity contribute to gamma diversity. Region X has high alpha diversity at its sites, but they are all fairly similar; the region thus has low beta diversity and only moderate gamma diversity. Region Y has low alpha diversity at its sites, but the sites differ from each other; the region therefore has high beta diversity, and higher gamma diversity than region X.

2.8.3 Value of Biodiversity

All species, communities and ecosystems have some economic values. These values are assessed in respect of: 1. anticipated/estimated price of an existing unutilized resource, i.e., in the process

of getting ready resources in their natural habitat. 2. selling (market) price of harvested resource, i.e., ready to sell resource, and 3. anticipated future price of resources. The value of biodiversity may have its value in different sense. These may be direct value (consumptive and productive use value) and indirect value (non-consumptive use value).

Direct values

Also known as use values and commodity values, these values are assigned to the products harvested by people. Direct values can be readily estimated by observing the activities of representative groups of people, monitoring collection points for normal products and examining the export/import statistics. These are obtained on their destruction. These values can be further subdivided as: (i) Consumptive use value: It can be assigned to goods such as vegetables and fuel

wood that are purchased and consumed locally and do not figure in national and international market. They do not appear also in Gross Domestic Product (GDP).

(ii) Productive use value: It is assigned to products that are derived from the wild and sold in commercial markets, both national as well as international markets, e.g., textile and leather industry.

Indirect values

Indirect values are assigned to benefits by biodiversity that do not involve harvesting and destroying the natural resource. Such benefits include ecological benefits such as soil formation, nutrient cycling, waste disposal, air and water purification, education, recreation, future options for human beings, etc. Indirect value can be further sub-divided as:

Ecosystems 41

(iv) To preserve the biodiversity and minimize/avoid the extinction of species (v) To utilize the natural resources in a sustainable way. Conservation of biodiversity mainly centres upon the wildlife conservation. The wildlife can be conserved by protecting both the life of animals as well as plants. These are protected in safeguard habitats, e.g., zoos, national parks, sanctuaries, botanical gardens, biosphere reserves, etc. In this regard, following two approaches are adopted to conserve the wildlife in protected habitats.

In situ (or on situ) conservation

In this approach, the protection is given to wild flora and fauna, and not to the domestically used plants and animals. Hence, the species are conserved in their own natural ecosystems. However, if needed, they may also be conserved in artificial ecosystems favourable to them. In this approach, the emphasis is given to save either protected area or the endangered species, e.g., zoos and national parks.

Advantages

The in situ conservation approach is advantageous in many respects, but has certain limitations too. The plus points are: 1. Advantageous for long-term protection. 2. Natural ecosystems spread in larger area and hence provide a good opportunity

for conservation as well as evolution. 3. It is a cheaper means to protect the species in their natural habitat.Limitations: Proper protection against environmental pollution may not be enough in natural types of ecosystems. It is also desired that the protected habitats should not be used for profitable activities, tourism and logging, etc. For example, the use of camels for tourism and elephants for logging should be discouraged, otherwise the objective of biodiversity conservation can be defeated.

Ex situ conservation

In this approach, the protection is given to the endangered and rare species in a man-made habitat, other than their natural ecosystems. To accomplish this, the species are protected in artificial conditions under the supervision of biodiversity conservation experts. To execute the process of protection, the endangered plant species are collected together and made to breed under desired conditions in seed banks and botanical gardens. Similarly, the endangered species are collected in zoo.

Advantages

The ex situ conservation is advantageous in following respect: 1. Long-term conservation 2. Due to controlled supervision, better food (assured food), better shelter and

security, the species can survive longer and may breed more offspring than usual.

3. The quality of offspring may be improved by genetic techniques, if so required.


4. Breeding of hybrid species is possible. 5. The captive breeding can be over-exploited to yield an increased number of

offspring, which may later be sent back to their natural ecosystems.

Limitations/disadvantages 1. Not a viable option for the protection of rare species due to human interference 2. Can be adopted for only a few kinds of species 3. Over-protection may result in the loss of naturality 4. Possible extinction of species due to: • Breeding in a changed environment • Demographic variations • Deteriorated quality of living • Uneasiness in the presence of exotic species The ex situ conservation can be more effectively utilized by exposing the species to varying natural environment, thereby restraining them to elope.

Major problems with biodiversity conservation (i) Low priority for conservation of living natural resources (ii) Exploitation of living natural resources for monetary gain (iii) Values and knowledge about the species and ecosystem inadequately known (iv) Unplanned urbanization and uncontrolled industrialization.

Major biodiversity threats (detail) (i) Habitat destruction (ii) Extension of agriculture (iii) Filling up of wetlands (iv) Conversion of rich biodiversity site for human settlement and industrial

development (v) Destruction of coastal areas (vi) Uncontrolled commercial exploitation

2.8.5 India as a Mega Biodiversity Nation

India has a very rich heritage of biodiversity at all three levels, viz., genes, species and ecosystem. Its richness may be assessed from the fact that it represents almost all the biogeographical regions of the world. The unique richness of its biodiversity covers a wide spectrum of habitats ranging from the rainforests to alpine vegetation, and coastal wetlands to deserts and mountains, etc. Due to the presence of a very large number of diverse species, India is referred to as mega diversity nation.Salient Features: Salient features of India’s biodiversity may be enumerated as follows: 1. Ranking: It ranks twelfth amongst the list of mega diversity nations of the world.

Ranking in other respects are:

Ecosystems 43

(i) In plant diversity: fourth in Asia and tenth in the world (ii) In mammals diversity: tenth in the world (iii) In endemic vertebrate diversity: eleventh in the world (iv) Agriculture and animal husbandry: seventh in the world

2. Land: Its land area is about 2.4% of the total land area of the world.

3. Biodiversity share: Its biodiversity contribution is about 8.22% of the total global biodiversity. Other contributions are:

(i) faunal contribution is about 7.31% of the total global fauna (ii) floral contribution is about 10.88% of the total global flora

4. Plants diversity: Plant diversity is high in bryophyte, angiosperms, family orchidaceae, etc. There are 47,000 species of plants.

5. Animal diversity: It is too high in insects. 81,000 species of animals are identified which includes 372 mammals, 1,228 birds, 428 reptiles, 204 amphibians and 2,546 fishes.

6. There are 33 Botanical Gardens, 89 National Parks, and 275 Zoos in India.

7. India is home to five world heritage sites: (i) Kaziranga National Park—Assam (ii) Ghana National Park—Rajasthan (iii) Manas Wildlife Sanctuary—Assam (iv) Nanda Devi National Park—Uttarakhand (v) Sunderban National Park—W.B. 8. Marine biodiversity: India’s marine biodiversity is too rich along its 7,515 km long

sea coastline. Its other related details are as under: (i) There are about 16,000 zooplankton species. (ii) There are more than 30 species of mangrove algae, 14 species of sea grass, 45

species of mangrove plants, and 342 species of corals. (iii) Mainly the polychaeta, molluscus and crustacean constitute the fauna. Their

share is about 60%, 20% and 20%, respectively. (iv) There is a biomass of about 12 gm/m2. (v) The estuaries, lagoons, mangroves and coral reefs ecosystems cover an area of

more than 200 million sq. km. 9. Agro-diversity: From the viewpoint of agricultural biodiversity, India ranks seventh

in the world. It is one of the 12 centres of origin of cultivated plants. An enormous variety of agro-products (grain + fruits + vegetable + others) is produced in India. It is estimated that 30,000 to 50,000 varieties of wheat, rice, pulse, sugar cane, potato, ginger, turmeric, banana, and pigeon-pea are produced here. Besides there are about 167 crop species and their wild relatives.

Ecosystems 45

Prevention and mitigation of natural disasters: Forests and grasslands protect landscapes against erosion, nutrient loss, and landslides through the binding action of roots. Ecosystems bordering regularly flooding rivers (floodplain forests and wetlands) help in absorbing excess water, and reducing the damage caused by floods. Certain coastal ecosystems (salt marshes, mangrove forests, etc.) prevent the erosion of coastlines.Provision of food security: Biodiversity provides the vast majority of our foodstuffs. The annual world fish catch, for example, (averaging 100 million metric tonnes), represents humanity’s most important source of wild animal protein, with over 20 per cent of the population in Africa and Asia dependent on fish as their primary source of protein. Terrestrial animals, meanwhile, supply an array of food products: eggs, milk, meat, etc. Wild biodiversity provides a wide variety of important foodstuffs, including fruits, game meats, nuts, mushrooms, honey, spices and flavorings. These wild foods are especially important when agricultural supplies fail. Indeed, wild biodiversity guards against the failure of even the most advanced agricultural systems. For example, the productivity of many of the developed world’s agricultural crops is maintained through the regular assimilation of new genes from wild relatives of these crops. These wild genes offer resistance to the pests and diseases that pose an ever-evolving threat to harvests.

2.8.7 The Biogeographic Classifi cation of India

Trans-Himalayas: An extension of the Tibetan plateau, harbouring high-altitude cold desert in Laddakh (J&K) and Lahaul Spiti (H.P.) comprising 5.7% of the country’s land mass.Himalayas: The entire mountain chain running from north-western to north-eastern India, comprising a diverse range of biotic provinces and biomes, 7.2% of the country’s land mass.Desert: The extremely arid area west of the Aravalli hill range, comprising both the salty desert of Gujarat and the sand desert of Rajasthan, 6.9% of the country’s land mass.Semi-arid: The zone between the desert and the Deccan plateau, including the Aravalli hill range, 15.6% of the country’s land mass.Western ghats: The hill ranges and plains running along the western coastline, south of the Tapti river, covering an extremely diverse range of biotic provinces and biomes, 5.8% of the country’s land mass.Deccan peninsula: The largest of the zones, covering much of the southern and southcentral plateau with a predominantly deciduous vegetation, 4.3% of the country’s land mass.Gangetic plain: Defined by the Ganges river system, these plains are relatively homo-genous, 11% of the country’s land mass.North-east India: The plains and non-Himalayan hill ranges of north-eastern India, with a wide variation of vegetation, 5.2% of the country’s land mass.Islands: The Andaman and Nicobar Islands in the Bay of Bengal, with a highly diverse set of biomes, 0.03% of the country’s land mass coasts. A large coastline distributed both


As regards the fauna, as many as 315 species of vertebrates belonging to 22 genera are endemic. These include 12 species of mammals, 13 species of birds, 89 species of reptiles, 87 species of amphibians and 104 species of fish. The extent of endemism is high in amphibian and reptiles. 117 species of amphibians are in the region, of which 89 species (i.e., 76%) are endemic. Of the 165 species of reptiles found in Western Ghats, 88 species are endemic. Many of the endemic and other species are listed as threatened. Nearly 235 species of endemic flowering plants are considered endangered. Rare fauna of the region includes Lion Tailed Macaque.(Fig. 2.13) Nilgiri Langur, Nilgiri Tahr, Flying Squirrel, and Malabar Gray Hornbill (Babu and Arora 1999).

Fig. 2.13 Lion tailed macaque

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Ecosystems and interdependence between the organisms and ... coastal estuary is subsidized by ... Ecosystems are composed of a variety of abiotic and biotic components that